362 Prof. Ayrton and Mr. Mather on Galvanometers. 



mirror. The record of this instrument is shown in line 4, 

 Table IT., and line 25 gives the record of another oscillograph 

 galvanometer by Messrs. Hotchkiss and Millis *. Both the 

 above instruments are of the moving magnet type with soft- 

 iron needles adopted for similar purposes by Blondel, Moler, 

 and others. Two other oscillographs are given in lines 4G and 

 47 of Table II., which are of the moving-coil type, and were 

 made by Mr. W. Duddell t of the Central Technical College. 

 For convenience of reference the principal numbers relating 

 to oscillographs are tabulated separately below, reductions 

 being made to a constant period of a thousandth of a second, 

 instead of 10 seconds, and the deflexions stated in terms of an 

 ampere, instead of a microampere. 



Table IV. 



Description. 



t. 



/• 



r. 



41 



270 



13 



2-08 



I approxi- 

 mately. 



djrh. 



d/rl 



Hotchkiss and Millis' 

 galv., 1895 



0256 



0-377 

 0-358 

 0093 



31 



1400 

 156 

 420 



2 2X10" 6 



lOxlO" 6 



30 Xl0~ 6 



6 xlO-8 



228 



600 



1070 



33,000 



263 



1050 

 1090 



35.600 



1 



McXittrick's galv., 

 1896 



Dudctell's galv., 1S97 . 



„ 1898 . 



Explanation of Table IY. 



Column t gives the periodic time in thousandths of a second when tested. 

 „ / „ deflexion in divisions per ampere as tested when scale- 

 distance = 1000 scale-divisions. 

 „ r „ resistance of instrument in ohms. 



,, I „ moment of inertia of the moving systems in C.G.S. units 

 approximately. 

 Columns d/rl and d/rl give the deflexions per ampere when the periodic 

 time is one thousandth of a second and the resistance of 

 each instrument is one ohm. Column d/ri is based on 

 the assumption that the sensitiveness varies as the square 

 root of the resistance, whilst column d/ri assumes that 

 sensitiveness is proportional to the two-fifths power of 

 the resistance. 



* Phys. Review, vol. iii. p. 49. In Phys. Rev. vol. iv. p. 128, 

 Mr. Millis gives an account of another instrument of very short period. 

 Unfortunately the data are insufficient to permit of comparison with other 

 oscillographs. 



f See " Oscillographs/' Electrician, Sept, 10, 1897, p. 638. 



